GENERAL CONSIDERATIONS ON TRANSMULTIPLEXING EQUIPMENTS. (Geneva, 1980; further amended)

5i 7.9 Other terminal equipments Recommendation G.791 GENERAL CONSIDERATIONS ON TRANSMULTIPLEXING EQUIPMENTS (Geneva, 1980; further amended) The CCITT, considering the advantages offered in some cases by direct through-connection (without voice-frequency interfaces) from FDM signals to TDM signals and vice versa, recommends in such cases (1) the use of the transmultiplexing equipment described in Definition 4020 of Recommendation G.701; (2) Recommendation G.792 which contains the characteristics common to all transmultiplexing equipment; (3) Recommendation G.793 which concerns 60-channel transmultiplexers providing 2048 kbit/s signals and using A-law encoding; (4) Recommendation G.794 which concerns 24-channel transmultiplexers providing 1544 kbit/s signals and using µ-law encoding. 1 Complementary definitions 1.1 type P transmultiplexer (TMUX-P) A transmultiplexing equipment in which the analogue interface is made up of several groups. 1.2 type S transmultiplexer (TMUX-S) A transmultiplexing equipment in which the analogue interface is made up of one or more supergroups. 1.3 hierarchical transmultiplexer Fascicle III.4 Rec. G.791 1

A transmultiplexer in which the digital interfaces satisfy the provisions of Recommendations G.703 and G.704 and the analogue interfaces those of Recommendation G.233 [1]. 1.4 transmultiplexer channel A frequency band of 4000 Hz on the analogue side, corresponding to a bit rate of 64 kbit/s on the digital side, which permits the transmission of a signal limited to the telephone band 300-3400 Hz. Access may be gained to a given channel: either at the level of the time slot associated with the relevant channel of the TDM signal; or at the level of the frequency band ( f p, f p ± 000 Hz) of the FDM signal, f p being the virtual carrier frequency associated with the channel concerned. The + sign corresponds to the case of the base supergroup, the sign to the case of the base group. Note Correspondence between out-of-band signalling on the analogue side and channel associated signalling on the digital side will be covered in the Recommendations specific to the various transmultiplexers. 2 Fascicle III.4 Rec. G.791

2 Transmultiplexer application The application on transmultiplexers for the interconnection of digital and analogue networks is illustrated in Supplement No. 28. Reference [1] CCITT Recommendation Recommendations concerning translating equipments, Vol. III, Rec. G.233. Recommendation G.792 CHARACTERISTICS COMMON TO ALL TRANSMULTIPLEXING EQUIPMENTS (Geneva, 1980; further amended) The CCITT, recommends that the characteristics below be respected by all the transmultiplexing equipments defined in Recommendation G.791. Recommendation O.133 contains information about test equipment. Account should be taken of the measurement accuracy provided by test equipment designed in accordance with that Recommendation. The following specifications are based on ideal measuring equipment. Therefore, they do not include any margin for measurement errors. To avoid level errors produced as a result of the use of test frequencies which are sub-multiples of the PCM sampling rate, the use of integer sub-multiples of 8 khz should be avoided. Where a nominal reference frequency of 1020 Hz is indicated (measurement of attenuation/frequency distortion and adjustment of relative levels), the actual frequency should be 1020, +2 to 7 Hz in accordance with Recommendation O.6 [18]. 1 Coding law Transmultiplexers should satisfy Recommendation G.711, 3. 2 Sampling rate of PCM channels Fascicle III.4 Rec. G.792 3

2. The nominal sampling rate of PCM channels is 8000 Hz ± 0 10 D lf261 6 according to Recommendation G.711, 3 Amplitude limitation of PCM channels In accordance with Recommendation G.711, 4, the theoretical load capacity of PCM channel is +3.14 dbm0 for the A-law and +3.17 dbm0 for the µ-law. 4 Accuracy of the analogue virtual carriers The analogue virtual carriers should satisfy the Recommendation cited in [1]. 5 Saturation level at the input of the analogue group The transmultiplexers should be able to accept at their analogue inputs, levels corresponding to the equivalent peak powers defined in Table 3/G.223 [5] (for example, +19 dbm0 for a group and +20.8 dbm0 for a supergroup). 4 Fascicle III.4 Rec. G.792

Note Attention is drawn to the possibility of using a transmultiplexer on the interpolated side of a digital speech interpolation (DSI) device. Given an interpolation rate of 2, this would lead to equivalent peak powers of 19.5 dbm0 for TMUX-P and 21.2 dbm0 for TMUX-S (see Table 3/G.223 [5]). 6 Methods of measuring quality in the audio band The various possible methods of measuring quality characteristics in the audio band are indicated in Figure 1/G.792. figure 1/G.792 p. 1 Fascicle III.4 Rec. G.792 5

When method B cannot be used because it requires digital signal generators and analyzers, which certain Administrations do not yet possess, method C can be used provisionally [looping of the digital ports, use of the terminals of auxiliary analogue channels (and possibly group modulators), assumption of the additivity of impairments and deduction of the impairments at the terminals of the channels (and possibly modulators) previously measured]. Method D corresponds in fact to four possible methods, depending on whether the emission of the test signal and its detection takes place on the analogue side or the digital side. Methods E and F are used for crosstalk measurements For the sake of the convenience and precision of the measurements, it is desirable that the regulation, when included in the transmultiplexer, can be blocked with a gain equal to unity. The specifications in 7 to 23 assume such blocking. 7 Attenuation distortion in the voice-frequency band as a function of frequency The measuring method is method A. The variation of the attenuation of each channel of a transmultiplexer as a function of frequency must remain within the limits of the mask in Figure 2/G.792. The level of emission is 10 dbm0; the reference frequency is 1020 Hz. 8 Group delay 8.1 Absolute value of the group delay The measuring method is method A. The absolute value of group delay defined as the minimum value of group delay in the speech band 300-3400 Hz should remain less than 3 ms for all the channels of a transmultiplexer. Note When the transmultiplexer is used for satellite digital communication at the earth station the minimum value of the group propagation time in the audiofrequency band may be increased from 3 ms to 6.5 ms. In all other cases, the value of 3 ms should be complied with. 6 Fascicle III.4 Rec. G.792

figure 2/G.792 p. 2 Fascicle III.4 Rec. G.792 7

8.2 Group-delay distortion The measuring method is method A. The group-delay distortion should not exceed the limits of the mask in Figure 3/G.792. The minimum group delay is taken as a reference; the power level at the input is 0 dbm0. Figure 3/G.792, p. 9 Noise 9.1 Idle channel noise, with all channels idle The measuring method is method B. When a PCM signal corresponding to amplitude 0 for the µ-law and the number 1 for the A-law in all channels of the transmultiplexer is applied to the digital input of the transmultiplexer, the psophometric noise measured over any channel at the digital output should not exceed 65 dbm0p. The measurement is conducted in the presence of pilots. 9.2 Channel noise, with all channels loaded except the one measured The measuring method is method A. In this case an intermodulation measuring set-up using the white noise method is employed, as described in the Recommendation cited in [6]. The level of emission of the noise signal being equal to the conventional load of the FDM signal considered (the Recommendation cited in [7]: 3.3 dbm0 for the group, 6.1 dbm0 for the supergroup), the noise measured in any given measuring slot should not exceed 62.5 dbm0p (i.e., 60 dbm0 in a 3100 Hz band). The centre frequencies of the specified measuring slots (CCITT Recommendation G.230 [8] and CCIR Recommendation 482 [9]) applicable to the transmultiplexers are: for the base group: 70 and 98 khz for the base supergroup: 394 and 534 khz. This measurement is carried out without emitting pilots or out-of-band signalling. 8 Fascicle III.4 Rec. G.792

9.3 Single frequency noise outside the band 300-3400 Hz The measuring method is B. When a PCM signal corresponding to amplitude 0 for the µ-law and amplitude 1 for the A-law in all channels is applied to the digital input of the transmultiplexer, the noise over any frequency should not exceed 50 dbm0 with the exception of the frequency of 80 Hz where it should not exceed 40 dbm0. 9.4 Idle noise in the PCM FDM direction all channels idle The measuring method is method D. A PCM signal, amplitude 0 for the µ-law and 1 for the A-law is applied at the digital input of the transmultiplexer in all channels. The power of the noise measured at the analogue output in any channel must be less than 70 dbm0p. Note White noise is assumed, and to take account of the psophometric weighting, the measurement can be made in a band of 1740 Hz, centred on the odd multiples of 2 khz. The measurement may be difficult in certain channels due to the presence of pilots. 10 Intermodulation The measuring method is method A. If two sine-wave signals of different frequencies f 1 and f 2 belonging to the band 300-3400 Hz of the channel considered, having no harmonic relation and of equivalent levels in the 4 to 21 dbm0 range, are applied simultaneously to the analogue ports of the transmultiplexer, there should be no intermodulation product of the type 2 f 1 f 2 of a level higher than 35 db with respect to the level of one of the two input signals. 11 Total distortion including quantizing distortion The measuring method is method B (or provisionally method C). If method B is used, the test signal is generated digitally and is therefore affected by theoretical quantizing distortion. A choice between the two following methods is recommended: Method 1 The signal-to-total distortion ratio measured according to method 1 described in 8 of Recommendation G.712 should respect the mask of Figure 4/G.792. The mask is to be complied with by all channels of the transmultiplexer. Method 2 With a sine-wave signal at a frequency between 700 and 1100 Hz or 350 and 550 Hz (e.g. 420 ± 20 Hz) (except for submultiples of 8 khz) being applied in the channel concerned at the digital input of the transmultiplexer, the ratio of signal-to-total distortion power, measured with appropriate noise weighting (see the Recommendation cited in [10]), should be below the limits of the mask represented in Figure 5/G.792. The mask is to be complied with by all the channels of the transmultiplexer. 10 Fascicle III.4 Rec. G.792

12 In-band spurious signals The measuring method is method A. The transmultiplexers must meet the provisions of Recommendation G.712, 9. 13 Variation of gain with the input level The measuring method is method A, the pilots being present at the analogue input. With a sine-wave signal at a frequency between 700 and 1100 Hz (except for submultiples of 8 khz) and a level between 55 and +3 dbm0 being applied in the channel concerned at the analogue input of the transmultiplexer, the variation of gain with respect to its value for an input level of 10 dbm0 should remain between the limits of the mask shown in Figure 6/G.792. The mask is to be complied with by all channels of a transmultiplexer. Fascicle III.4 Rec. G.792 11

12 Fascicle III.4 Rec. G.792 figure 4/G.792 p. 4

figure 5/G.792 p. 4 Fascicle III.4 Rec. G.792 13

figure 6/G.792 p. 6 14 Crosstalk For measuring crosstalk, two transmultiplexers must be connected back-to-back (methods E and F). There are two possible configurations and four possible measurements (see Figure 7/G.792): far-end crosstalk digital to digital (see Note 1) near-end crosstalk digital to digital (see Note 1) far-end crosstalk analogue to analogue near-end crosstalk analogue to analogue 14.1 Intelligible crosstalk When a sine-wave signal between 700 and 1100 Hz and with a level of 0 dbm0 is injected in any channel on the digital or analogue side of the transmultiplexer, the crosstalk ratio between the signal channel and any other channel must be greater than 65 db for any of the four crosstalk contributions identified above (see Note 2). 14.2 Unintelligible crosstalk When a conventional telephone signal according to Recommendation G.227 [11], is injected in any channel on the digital or analogue side of the transmultiplexer, at a level of 0 dbm0, the level of crosstalk measured in any other 14 Fascicle III.4 Rec. G.792

channel for any of the four crosstalk contributions identified above must be below 60 dbm0p (see Note 3). Note 1 In this configuration, the two transmultiplexers are connected at the level of the analogue FDM signal and there will generally be a problem of level adaptation between the send and the receive sides. This can be solved with the use of attenuators or amplifiers of appropriate gain. Attention must be given on the risk of introduction of additional crosstalk in these complementary devices. It should be desirable to include the level adaptation facilities in the transmultiplexer itself. Fascicle III.4 Rec. G.792 15

Note 2 In order to overcome fundamental gain enhancement effects associated with PCM encoders, which can mask the true crosstalk, measuring methods using activating signals based on those defined in Recommendation G.712 can be used. Note 3 Recognizing the difficulty of generating conventional telephone signals according to Recommendation G.227 in a suitable format for insertion into either the analogue or digital input to the transmultiplexer, it shall be adequate to demonstrate, via suitable single frequency crosstalk tests, that the intent of the above specification is met, without actually using a conventional telephone signal. Figure 7/G.972, p. 15 Go-to-return crosstalk For measuring go-to-return crosstalk, two transmultiplexers must be connected back-to-back (methods E and F). There are two possible configurations and two possible measurements (see Figure 7b/G.792): near-end crosstalk digital to digital (see Note 1 of 14); near-end crosstalk analogue to analogue. When a sine-wave signal between 300 and 3400 Hz and with a level of 0 dbm0 is injected in any channel on the digital or analogue side of the transmultiplexer, the crosstalk ratio between the signal channel and the associated return channel must be greater than 58 db for each contribution identified above. When using method F, a PCM signal corresponding to amplitude 0 for the µ-law and amplitude 1 for the A-law, should be inserted into the digital input of all return channels. Note Concerning the activating signal for method F, see Recommendation G.712, 10. 16 Variation of the equivalent of the channels within the FDM assembly Measuring method A. When a test tone at the equivalent of 1020 Hz in any channel, and with a level of 10 dbm0 is applied to the analogue input of the transmultiplexer, the level measured at the analogue output of the transmultiplexer shall be within a tolerance of ± db of the level measured when that test tone is applied at the equivalent of 1020 Hz in the channel containing the reference pilot of the FDM assembly considered. 16 Fascicle III.4 Rec. G.792

17 Adjustment of the relation between the coding law and the analogue level Measuring method D. To measure the correspondence between the coding laws and the analogue levels, the sequence of character signals from Table 5/G.711 for the A-law and from Table 6/G.711 for the µ-law may be applied periodically at the digital input of the transmultiplexer: the signal at the analogue output of the transmultiplexer should correspond to a sine-wave signal of frequency 1 khz in the corresponding channel at a level between 0.5 and +0.5 dbm0. Fascicle III.4 Rec. G.792 17

Note The use of another digital periodic sequence representing a nominal reference frequency of 1020 Hz at a nominal level of 0 dbmo is acceptable, provided that the theoretical level accuracy is better than ±.03 db. To check the load capacity of the PCM coder contained in the transmultiplexer, a sine-wave signal at a nominal frequency of 1020 Hz can be applied for any channel at the analogue input of the transmultiplexer. Initially the level of this signal is considerably below the load capacity, then it is raised gradually. Note is taken of the input level at which the character signal corresponding to the extreme quantization interval for positive and negative amplitudes first appears at the digital output in the channel considered. The load capacity is then taken to be equal to this input level, increased by 0.3 db. The values obtained for the various channels should be between 2.64 and 3.64 dbm0 for the A-law and between 2.67 and 3.67 dbm0 for the µ-law. 18 Carrier leak at the analogue ports Measuring method A, the analogue input of the transmultiplexer being looped to its nominal impedance. The transmultiplexers should meet the provisions of the Recommendation cited in [12]. 19 Protection against out-of-band signals at the analogue ports 19.1 Out-of-band spurious signals at the analogue output The measuring method is C for the TMUX-P, range a) (see below), otherwise A. The test signal has a level of 0 dbm0. For the TMUX-P, range a), a signal according to Recommendation G.227 is used, otherwise a sine-wave signal (300 to 3400 Hz). The level of supurious signals outside the group or supergroup band ( f 1 to f 2 ) at the analogue output should not exceed the following limits: TMUX-P a) f 1 > f x > ( f 1 4 khz) 60 dbm0p and f 2 < f x < ( f 2 + 4 khz) (Note 1) b) ( f 1 4 khz) > f x > ( f 1 12 khz) 70 dbm0 and ( f 2 + 4 khz) < f x < ( f 2 + 12 khz) (Note 2) c) f x ( f 1 12 khz) and 80 dbm0 f x " ( f 2 + 12 khz) TMUX-S a) f x = f 1 4 khz 60 dbm0 and f x = f 2 + 4 khz (Note 3) b) ( f 1 8 khz) > f x > ( f 1 20 khz) 70 dbm0 and 18 Fascicle III.4 Rec. G.792

( f 2 + 8 khz) < f x < ( f 2 + 20 khz) (Note 2) c) f x ( f 1 20 khz) and 80 dbm0 f x " ( f 2 + 20 khz) Note 1 Telephony channels, pilots or additional test frequencies are possible in this frequency range. Note 2 Adjacent carrier-frequency sound-programme channels may begin in this range (with reduced requirements). Note 3 This range may contain pilots or additional measuring frequencies. Fascicle III.4 Rec. G.792 19

19.2 Crosstalk due to out-of-band signals at the analogue input Measuring methods C and A, respectively (see 19.1). With test signals as in 19.1 in a channel of an adjacent FDM assembly, the level at the transmultiplexer output should not exceed the following limits: TMUX-P a) f 1 > f x > ( f 1 4 khz) 60 dbm0p and f 2 < f x < ( f 2 + 4 khz) (Note) b) f x < ( f 1 4 khz) 70 dbm0 and f x > ( f 2 + 4 khz) (Note) TMUX-S a) f x = f 1 4 khz 50 dbm0 and f x = f 2 + 4 khz (Note) b) f x < ( f 1 8 khz) 70 dbm0 and f x > ( f 2 + 8 khz) (Note) Note For this measurement, a low-level auxiliary signal is injected into the disturbed channel. The appropriate auxiliary signal is a sine-wave signal between 33 and 40 dbm0. The frequency and characteristics of the filter in the measuring equipment must be carefully selected to ensure that the auxiliary signal does not appreciably reduce the accuracy of the crosstalk measurement. 20 Protection and suppression of pilots Measuring method D. The transmultiplexers should meet the provisions of the Recommendation cited in [14]. 21 Protection and suppression of out-of-band signalling 21.1 Protection of the out-of-band signalling channel for transmultiplexers using signalling system R2 Measuring method D. When a transmultiplexer is capable of emitting out-of-band signalling waves at frequency 3825 Hz, it should meet the provisions of Recommendation Q.414 [15], Figure 6/Q.414 being replaced by Figure 7/G.792. The measuring method associated with the latter figure is recalled in Note 1. Note 1 The signalling channel must be protected at the sending end against disturbance from the associated and the adjacent channel. When a sine-wave at 0 dbm0 level is applied to the digital input of the associated channel, the level measured at the analogue output of the transmultiplexer must not exceed the levels shown in Figure 8/G.792. 20 Fascicle III.4 Rec. G.792

When a sine-wave of frequency f is applied to the digital input of the adjacent channel, it produces two signals that appear on the frequency scale of Figure 8/G.792 as having the frequencies (4000 + f ) and (4000 f ). The level of the (4000 + f ) signal measured at the analogue output of the transmultiplexer shall not be higher than 33 dbm0, when the sine-wave with frequency f is applied to the digital input of the adjacent channel at a level shown in Figure 8/G.792 for the frequency of (4000 + f ). The level of the (4000 f ) signal, measured at the analogue output of the transmultiplexer, shall not be higher than 33 dbm0, when the sine-wave with frequency f is applied to the digital input of the adjacent channel at any level below the value shown in Figure 8/G.792 for the frequency (4000 f ). 21.2 Disturbance of telephone channels by out-of-band signalling frequency for transmultiplexers using signalling system R2 The measuring method is method B or D. Interference at 175 Hz and 3825 Hz should not exceed 53 dbm0 respectively 63 dbm0 when a continuous tone of 3825 Hz with a nominal level of 20 dbm0 is applied to all channels. These values correspond to a contribution to the channel noise in the order of 73 dbm0p (design objective). Fascicle III.4 Rec. G.792 21

Figure 8/G.792, p. 21.3 Other out-of-band signalling systems See Annex A. 22 Mutual interference between pilots and out-of-band signalling The transmultiplexers capable of emitting and receiving out-of-band signalling should meet the provisions of the Recommendation cited in [17]. 23 Short- and long-term variation of loss with time The measuring method is A. When a sine-wave signal at level 10 dbm0 and at a nominal frequency of 1020 Hz is applied at the analogue input of the transmultiplexer, the level measured at the analogue output should not vary by more than ±.2 db during 10 consecutive minutes of normal operation, more than ±.5 db during 3 consecutive days nor by more than ± db for one year, allowing for the authorized variations of power supply, voltages and temperature. ANNEX A (to Recommendation G.792) Out-of-band signalling systems using a burst-mode method The possibility of such systems is mentioned in Annex A to Recommendation Q.21 and Annex B to Recommendation G.232. These annexes should be taken into consideration. When a transmultiplexer is capable of converting such systems, the following applies: Signalling frequency at the sending point: 3825 Hz ± 4 Hz. Send level of the signalling frequency: 5 dbm0 ± 1 db. 22 Fascicle III.4 Rec. G.792

Protection of the out-of-band signalling channel: see Figure 8/G.792. Disturbance of telephone channels by the out-of-band signalling frequency: the measuring method is method B. Channel noise should not exceed 63 dbm0p in the call channel (continuous tone). In the adjacent channel (the closest to the signalling frequency) likewise 63 dbm0p burst or continuous tone. In every other channel 76 dbm0p burst or continuous tone. Fascicle III.4 Rec. G.792 23

Note 1 Burst tones do not occur in the call channel after call set-up has taken place. Note 2 Burst rates are in the order of 10 to 25 Hz. Note 3 Charge metering pulses are of long duration, e.g. 150/450 ms and are evaluated as a continuous tone. References [1] CCITT Recommendation Recommendations relating to the accuracy of carrier frequencies, Vol. III, Rec. G.225, 1. [2] CCITT Recommendation Pilots on groups, supergroups, etc., Vol. III, Rec. G.241, 1. [3] Ibid., 2. [4] Ibid., 3. [5] CCITT Recommendation Assumptions for the calculation of noise on hypothetical reference circuits for telephony, Vol. III, Rec. G.223, Table 3/G.223, 6. [6] CCITT Recommendation Measurement of circuit noise in cable systems using a uniform-spectrum random noise loading, Vol. III, Rec. G.228, A.1, A.2.2. [7] CCITT Recommendation Assumptions for the calculation of noise on hypothetical reference circuits for telephony, Vol. III, Rec. G.223, 2.1. [8] CCITT Recommendation Measuring method and through-connection filters for noise produced by modulating equipment, Vol. III, Rec. G.230. [9] CCIR Recommendation Measurement of performance by means of a signal of a uniform spectrum for systems using frequency-division multiplex telephony in the fixed satellite service, Vol. IV, Rec. 482, ITU, Geneva, 1978. [10] CCITT Recommendation Assumptions for the calculation of noise on hypothetical reference circuits for telephony, Vol. III, Rec. G.223, 7. [11] CCITT Recommendation Conventional telephone signal, Vol. III, Rec. G.227. [12] CCITT Recommendation 12-channel terminal equipments, Vol. III, Rec. G.232, 5.1, 5.2. [13] CCITT Recommendation Through-connection of groups, supergroups, etc., Vol. III, Rec. G.242, 1. [14] CCITT Recommendation 12-channel terminal equipments, Vol. III, Rec. G.232, 12.1, 12.2 and Annex A. [15] CCITT Recommendation Signal sender, Vol. VI, Rec. Q.414, Figure 6/Q.414. [16] CCITT Recommendation 12-channel terminal equipments, Vol. III, Rec. G.232. [17] Ibid., 12.3 and Annex B. [18] CCITT Recommendation 1020 Hz reference test frequency, Vol. IV, Rec. O.6. Recommendation G.793 CHARACTERISTICS OF 60-CHANNEL TRANSMULTIPLEXING EQUIPMENTS (Geneva, 1980; further amended) 24 Fascicle III.4 Rec. G.793

1 Introduction The 60-channel transmultiplexer is a transmultiplexing equipment which satisfies Recommendations G.791 and G.792 and provides interconnection between two digital signals at 2048 kbit/s and an analogue supergroup (60-channel TMUX-S). 2 Digital interfaces 2.1 Coding law The coding law used is A-law specified in Recommendation G.711. 2.2 Interfaces The 2048-kbit/s interfaces satisfy Recommendation G.703, 6. Fascicle III.4 Rec. G.793 25

2.3 Frame structure The structure is specified in Recommendation G.704, 3.3.1. The strategy and the criteria for loss and recovery of frame alignment satisfy Recommendation G.706, 4.1. 2.4 Multiframe structure The multiframe structure of time slot 16 satisfies Recommendation G.704, 3.3.3. The strategy and the criteria for loss and recovery of multiframe alignment satisfy Recommendation G.732, 5.2. 3 Analogue interfaces 3.1 Ports The analogue interface consists of a 60-channel supergroup (band 312-552 khz) which satisfies Recommendation G.233 [1]. The preferred signal levels at the supergroup distribution frame should be: for sending 36 dbr for receiving 30 dbr The impedances are: 75 ohms (unbalanced). 3.2 Pilots The 60-channel transmultiplexer should transmit the following pilots: TMUX-S: A supergroup pilot with a frequency 411 20 Hz and a level of 20 dbm0, one pilot per group with a level of 20 dbm0 and frequencies of: Group 1: 335 20 Hz Group 2: 383 20 Hz Group 3: 431 20 Hz Group 4: 479 20 Hz Group 5: 527 20 Hz The transfer of pilot alarms individually for each group in a supergroup and the consequence for the split channels of group 3 can be seen in Figure 1 of Supplement No. 32. Other sets of pilots as recommended in Recommendation G.241 can be used. Special attention should be given to the compatibility of the set of pilots adopted with the out-of-band signalling system using a frequency at 3825 Hz. 26 Fascicle III.4 Rec. G.793

The characteristics relating to the generation and transmission of these pilots are given in Recommendation G.241 [2]. 3.3 Pilot detection and regulation The transmultiplexer may or may not regulate levels on the basis of the levels of the group and supergroup pilots. If so, the transmultiplexer must meet the conditions of the Recommendation cited in [2]. Detection of the levels of the group pilots and or supergroup mentioned in 3.2 should, however, be effected to ensure operation of the interruption control system (Recommendation Q.416 [3]), when R2 signalling is used. 4 Correspondence between analogue and digital channels A fixed correspondence is established between the analogue and digital channels. The correspondence shown in Table 1/G.793 (which facilitates the transfer of alarms and results in a natural order of the channels on the analogue side) is recommended. Fascicle III.4 Rec. G.793 27

H.T. [T1.793] TABLE 1/G.793 PCM 1 channels 1 to 12 Group 1 312-360 khz PCM 1 channels 13 to 24 Group 2 360-408 khz PCM 1 channels 25 to 30 Group 3 408-432 khz PCM 2 channels 1 to 6 Group 3 432-456 khz PCM 2 channels 7 to 18 Group 4 456-504 khz PCM 2 channels 19 to 30 Group 5 504-552 khz } Note In national networks or by agreement between Administrations, other schemes of correspondence between analogue and digital channels may be used. Table 1/G.793 [T1.793], p. 5 Plesiochronous operation of incoming PCM streams Sixty-channel transmultiplexers should be able to accept two mutually plesiochronous incoming PCM streams within the limits laid down in Recommendation G.703 (bit rate 2048 kbit/s, ± 0 (mu 0 D lf261 6 ). In the case of transmultiplexers with digital filtering, this means that the two input ports at 2048 kbit/s are fitted with frame aligners (jump or repetition of samples) and multiframe aligners for synchronizing the incoming PCM streams with the transmultiplexer clock. In order to avoid a major slip frequency, the two incoming PCM streams should be either synchronous with the transmultiplexer or plesiochronous with each other and with the transmultiplexer clock, so that Recommendation G.811 on the plesiochronous network is satisfied. 6 Synchronization of transmultiplexer The transmultiplexer must produce virtual analogue carrier frequencies with the accuracy specified in Recommendation G.225 [4] (± 0 D lf261 7 ). For this purpose, it is recommended: a) either that the transmultiplexer should have an internal clock of sufficient accuracy; b) or that the transmultiplexer should be synchronizable with an external signal which may be: 1) a frequency (see Note 3) produced by a central FDM generator: 4, 12 or 124 khz; 2) or one of the incoming PCM streams which has sufficient accuracy (this may be the case, for example, when this PCM stream at 2048 kbit/s is produced by a TDM switching equipment). If both 2048-kbit/s streams are of sufficient accuracy, the use of PCM stream No. 1 is preferred. In most cases this avoids, at the digital filtering transmultiplexer input, the slipping phenomena which, when too frequent, cause high error rates on in-band data signals. 28 Fascicle III.4 Rec. G.793

Note 1 In the case of a digital filtering transmultiplexer, when synchronization on one of the incoming PCM streams is not possible, the remote digital terminal should have the sending side synchronized with the receiving side so as to avoid slipping at the transmultiplexer input. Note 2 In the case of external synchronization, transmultiplexers often have an internal oscillator locked to the external signal. If, upon loss of the external sync signal, this internal oscillator is allowed to continue to supply the clock for the outgoing digital signal (now in the free-running mode), then this oscillator should have a minimum free-running accuracy of 50 10 D lf261 6. This is intended to allow the distant end digital terminal to receive an adequate frequency for alarm purposes only, so as not to confuse maintenance and trouble-shooting activities. Also, a local alarm should be given in the event of a fault in the synchronization system or in the absence of the external synchronization signal (Tables 2/G.793, 3/G.793 and 2 of Supplement No. 32). Note 3 In the case where the transmultiplexer is to be used in a TDMA satellite application, the effect of the satellite Doppler frequency variation must be taken into account. This can be done in two ways: either, the TDMA terminal incorporates the Doppler buffer memories of appropriate capacity in the earth station to satellite direction. In this case, the two directions of the TMUX must be synchronized from one of the two 2048 kbit/s PCM streams transmitted by the TDMA receive terminal; or, the TDMA terminal does not incorporate Doppler buffers. In this case, the PCM to FDM direction of the TMUX may be synchronized from one of the two 2048 kbit/s streams transmitted by the TDMA receive terminal. In the FDM to PCM direction, the 2048 kbit/s streams transmitted by the TMUX must be made synchronous with the TDMA system transmit clock: this supposes that a synchronization signal (contradirectional with the data) is provided by the TDMA transmit terminal to the TMUX. In the case where the processing in a digital filtering transmultiplexer is made synchronously for the two directions, Doppler buffer memories of appropriate capacity must be incorporated in the PCM interfaces. 7 Signalling Different kinds of signalling systems can be envisaged. 7.1 In-band signalling The 60-channel transmultiplexer is transparent for channel-associated in-band signalling. 7.2 Common channel signalling In the case when common channel signalling must be routed through the transmultiplexer, attention is drawn to the fact that the transmission capabilities of a channel in the transmultiplexer is limited to the band 300-3400 Hz (i.e. data rates corresponding to this frequency band). Information on signalling bit rates is given in 2 of Recommendation Q.702. In the opposite case, when common channel signalling is not routed through the TMUX, no special problems are recognized. 7.3 Out-of-band signalling As regards Signalling System R2, signalling conversion between the analogue and digital versions of line signalling as recommended in Recommendation Q.430 is to be used in the case of international interconnection and should conform to the following specifications. The transmultiplexer, or an additional equipment associated with it, converts the analogue version to the 2-bit digital version of the R2 line Signalling System, and vice versa. In all cases, the transmultiplexer should provide the following facilities for signalling: a) Analogue side 1) recognition of the signalling frequency at 3825 Hz in accordance with Recommendation Q.415 [5]; 2) transmission of the signalling frequency at 3825 Hz in accordance with Recommendation Q.414 [6]; Fascicle III.4 Rec. G.793 29

3) supervision of group pilots (and supergroup pilots if necessary) in accordance with Recommendation Q.416 [3]. 30 Fascicle III.4 Rec. G.793

b) Digital side 1) extraction of signalling bits a and b of time slots 16 received in accordance with the Recommendation cited in [7]; 2) insertion of appropriate signalling data in bits a and b of time slots 16 transmitted in accordance with the Recommendation cited in [7]; 3) detection of PCM system faults. The conversion between the analogue and digital versions of the R2 line Signalling System should be made in accordance with [8]. When the conversion is made in an external equipment, the transmultiplexer should supply the necessary ports. For national networks, a method of using the analogue line signalling version on both analogue and digital transmission systems is described in Supplement No. 32. 8 Fault conditions and consequent action 8.1 Principles of the action to be taken The principles governing the handling of alarms is as follows: The behaviour of a transmultiplexer vis-`a-vis a 30-channel PCM multiplex should be the same as that of another 30-channel PCM multiplex. However, the transmultiplexer performs certain functions peculiar to digital multiplexing equipments such as the transmission of the Alarm Indication Signal (AIS). Vis-`a-vis a group modulator, it should behave like another group modulator. The principles of alarm transfer are described in Supplement No. 32 which also contains particular solution used in national networks. 8.2 Digital version of R2 signalling system Table 2/G.793 summarizes the fault conditions and the consequent actions. 8.3 In-band signalling and common channel signalling Table 3/G.793 summarizes the fault conditions and the consequent actions (see Note). Note The problem of per channel alarm transfer needs further study. For applications where the TMUX is used in TDMA configuration, Recommendation Q.33 should be considered [11]. Fascicle III.4 Rec. G.793 31

Blanc 32 Fascicle III.4 Rec. G.793

H.T. [1T2.793] TABLE 2/G.793 Fault conditions and consequent actions, applicable if Signalling System R2 is used (see Note 1) } Consequent actions Fault conditions Loss of signal Error ratio > 10 D lf261 3 Loss of frame alignment (see Note 2) } Yes (see Note 3) Yes Yes PCM > FDM a=b=1 Loss of multiframe alignment (see Note 2) } Yes (see Note 3) Yes Reception of bit 3, time slot 0 or bit 6, time slot 16, frame 0 (see Note 2) } Absence of the received group pilot (see Note 5) } Yes Yes FDM > PCM Absence of pilot Yes (see Note 6 Absence of the received supergroup pilot (see Note 7) } Yes Pilot level deviation alarm (Note 8) } Yes Failure of power supply Yes Yes, if possible Yes, if possible System failure (see Note 9) Yes Yes Yes (see Note 6 Synchronization failure (see Note 10) } Yes Note 1 A Yes n the table signifies that an action should be taken as a consequence of the relevant fault conditions. An open space in the table signifies that the relevant action should not be taken as a consequence of the relevant fault condition, if this condition is the only one present. If more than one fault condition is simultaneously present, the relevant action should be taken if, for at least one of the conditions, a Yes is defined in relation to this action. Fascicle III.4 Rec. G.793 33

Pour Montage : System alarms FDM alarms PCM alarms Table 2/G.793 [1T2.793] (à l italienne), p. 34 Fascicle III.4 Rec. G.793

H.T. [2T2.793] Note 2 The fault conditions Loss of signal at 2 Mbit/s, Error ratio > 10 D lf261 3, Loss of frame alignment, Loss of multiframe alignment, Reception of bit 3, time slot 0, Reception of bit 6, time slot 16, frame 0 and the consequent action Bit 3, time slot 0 to 1, Bit 6, time slot 16, frame 0 to 1, Bit 6, time slot 16, frame 0 to 1 and AIS sent are defined in Recommendation G.732. Note 3 The 60-channel transmultiplexer should be able to detect the alarm indication signal (AIS) on incoming streams at 2048 kbit/s. When AIS is detected, the prompt maintenance indication associated with the loss of frame alignment, with an excessive error rate or with the loss of multiframe alignment should be blocked. Note 4 This action is not necessary when the digital version of Signalling System R2 is used, but may be useful with other applications. Note 5 The definition of absence of group pilot used for the operation of the interruption control system is given in the Recommendation cited in [9]. The supergroup pilot can also be used. Note 6 The AIS is sent only if the 30 channels of a single PCM stream are in the alarm condition. Note 7 Detection of absence of supergroup pilot is not obligatory. If the supergroup pilot is not sent, this alarm function can be performed by supervision of the 5 group pilots. Note 8 The concept of pilot level deviation alarm corresponds to a variation on the level of the pilot from its nominal value by more than ± db, as stated in [10]. This applies only to transmultiplexers with automatic internal level regulation. Note 9 The system fault condition corresponds to a fault on the transmultiplexer detected by the transmultiplexer s supervision system, when it has one. Note 10 The synchronization fault is that mentionned in 6 of Recommendation G.793. When the transmultiplexer is synchronized with an external signal or with one of two incoming PCM streams at 2048 kbit/s, the transmultiplexer should transmit an alarm signal in the event of synchronization loss. H.T. [1T3.793] TABLE 3/G.793 Fault conditions and consequent actions, applicable for in-band signalling and common channel signalling (Note 1) Fascicle III.4 Rec. G.793 35

Consequent actions Fault conditions Loss of signal Error ratio > 10 D lf261 3 Loss of frame alignment (see Note 2) } Yes (see Note 3) Yes Yes PCM > DM Yes (see Note 4) Absence of the received group pilot (see Note 5) } Yes Yes FDM > CM Yes (see Note 6) Absence of the received supergroup pilot (see Note 7) } Yes Pilot level deviation alarm (see Note 8) } Yes Failure of power supply Yes Yes, if possible Yes, if possible System Yes Yes, 5 groups Yes (see Note 7) Synchronization failure (see Note 10) } Yes Note 1 A Yes in the table signifies that an action should be taken as a consequence of the relevant fault conditions. An open space in the table signifies that the relevant action should not be taken as a consequence of the relevant fault condition, if this condition is the only one present. If more than one fault condition is simultaneously present, the relevant action should be taken if, for at least one of the conditions, a Yes is defined in relation to this action. Note 2 The fault conditions Loss of signal at 2 Mbit/s, Error ratio > 10 D lf261 3, Loss of frame alignment, and the consequent action Bit 3, time slot 0 to 1, and AIS sent are defined in Recommendation G.732. Note 3 The 60-channel transmultiplexer should be able to detect the alarm indication signal (AIS) on incoming streams at 2048 kbit/s. When AIS is detected, the prompt maintenance indication associated with the loss of frame alignment, with an excessive error rate should be blocked. Note 4 In the PCM FDM direction, the pilots must be cut for the 3 groups associated with a PCM multiplex signal in the event of the detection of a fault on the PCM multiplex signal stream. When a single PCM multiplex signal is faulty, this involves the blocking of 6 channels which are not faulty. 36 Fascicle III.4 Rec. G.793

Note 5 The definition of absence of group pilot used for the operation of the interruption control system is given in the Recommendation cited in [9]. The supergroup pilot can also be used. Note 6 The AIS is sent only if the 30 channels of a single PCM stream are in the alarm condition. Note 7 Detection of absence of supergroup pilot is not obligatory. If the supergroup pilot is not sent, this alarm function can be performed by supervision of the 5 group pilots. Pour Montage : System alarms IDM alarms PCM alarms Notes of the Table 2/G.793 [2T2.973], p. Fascicle III.4 Rec. G.793 37

H.T. [1T3.793] TABLE 3/G.793 Fault conditions and consequent actions, applicable for in-band signalling and common channel signalling (Note 1) Consequent actions Fault conditions Loss of signal Error ratio > 10 D lf261 3 Loss of frame alignment (see Note 2) } Yes (see Note 3) Yes Yes PCM > DM Yes (see Note 4) Absence of the received group pilot (see Note 5) } Yes Yes FDM > CM Yes (see Note 6) Absence of the received supergroup pilot (see Note 7) } Yes Pilot level deviation alarm (see Note 8) } Yes Failure of power supply Yes Yes, if possible Yes, if possible System Yes Yes, 5 groups Yes (see Note 7) Synchronization failure (see Note 10) } Yes Note 1 A Yes in the table signifies that an action should be taken as a consequence of the relevant fault conditions. An open space in the table signifies that the relevant action should not be taken as a consequence of the relevant fault condition, if this condition is the only one present. If more than one fault condition is simultaneously present, the relevant action should be taken if, for at least one of the conditions, a Yes is defined in relation to this action. Note 2 The fault conditions Loss of signal at 2 Mbit/s, Error ratio > 10 D lf261 3, Loss of frame alignment, and the consequent action Bit 3, time slot 0 to 1, and AIS sent are defined in Recommendation G.732. Note 3 The 60-channel transmultiplexer should be able to detect the alarm indication signal (AIS) on incoming streams at 2048 kbit/s. When AIS is detected, the prompt maintenance indication associated with the loss of frame alignment, with an excessive error rate should be blocked. 38 Fascicle III.4 Rec. G.793

Note 4 In the PCM FDM direction, the pilots must be cut for the 3 groups associated with a PCM multiplex signal in the event of the detection of a fault on the PCM multiplex signal stream. When a single PCM multiplex signal is faulty, this involves the blocking of 6 channels which are not faulty. Note 5 The definition of absence of group pilot used for the operation of the interruption control system is given in the Recommendation cited in [9]. The supergroup pilot can also be used. Note 6 The AIS is sent only if the 30 channels of a single PCM stream are in the alarm condition. Note 7 Detection of absence of supergroup pilot is not obligatory. If the supergroup pilot is not sent, this alarm function can be performed by supervision of the 5 group pilots. Pour Montage : System alarms IDM alarms PCM alarms Table 3/G.793 [1T3.793], p. Fascicle III.4 Rec. G.793 39

H.T. [2T3.793] Note 8 The concept of pilot level deviation alarm corresponds to a variation on the level of the pilot from its nominal value by more than ± db as stated in the Recommendation cited in [10]. This applies only to transmultiplexers with automatic internal level regulation. Note 9 The system fault condition corresponds to a fault on the transmultiplexer detected by the transmultiplexer s supervision system, when it has one. Note 10 The synchronization fault is that mentionned in 6 of the Recommendation G.793. When the transmultiplexer is synchronized with an external signal or with one of the two incoming PCM streams at 2048 kbit/s, the transmultiplexer should transmit an alarm signal in the event of synchronization loss. Pour Montage : System alarms IDM alarms PCM alarms H.T. [1T1.794] TABLE 1/G.794 Fault conditions and consequent action for the 24-channel transmultiplexer 40 Fascicle III.4 Rec. G.793

Consequent Action Fault Conditions } Prompt maintenance alarm indication (7) } Alarm indication to the remote equipment (3) } AIS sending (4) Blocking of faulty speech channels } Pilot cut-off to the remote FDM terminal } Loss of frame alignment and multiframe alignment or Loss of incoming signal (2) } Yes (8) Yes Yes (PCM > DM) Digital error ratio 10 D lf261 4 or 10 D lf261 3 (10) } Yes (8) Yes Reception of alarm indication from the remote equipment (2, 3) } Yes AIS receiving (4) Yes Yes (PCM > DM) Absence of group pilot (5) Yes Yes (9) Yes Pilot level deviation alarm (11) } Yes, if regulation is present Failure of power supply (2) Yes Yes, depending on network applications } System failure (6) Yes Yes, depending on network applications } Yes, depending on network applications } Yes, depending on network applications } Yes, depending on network applications } Synchronization failure Yes Note 1 A Yes in the table signifies that an action should be taken as a consequence of the relevant fault conditions. An open space in the table signifies that the relevant action should not be taken as a consequence of the relevant fault condition, if this condition is the only one present. If more than one fault condition is simultaneously present, the relevant action should be taken if, for at least one of the conditions, a Yes is defined in relation to this action. Fascicle III.4 Rec. G.793 41

Note 2 The fault conditions Loss of incoming signal, Loss of frame alignment and multiframe alignment, Reception of alarm indication to the remote equipment and Failure of power supply are defined in Recommendation G.733. Note 3 For Alarm indication to the remote equipment, data link bits are used. Note 4 The AIS can be used only in the new frame structure to be specified by Study Group XVIII. Note 5 The level, at which Absence of group pilot is detected, is under study. Note 6 The System failure, which is only for the digital filtering transmultiplexer, corresponds to a fault detected by the transmultiplexer s supervision system, when it has one. Note 7 The consequent action Prompt maintenance Alarm indication and Alarm indication to the remote equipment are defined in Recommendation G.733. Notes of the Table 3/G.793 [2T3.793], p. References [1] CCITT Recommendation Recommendations concerning translating equipments, Vol. III, Rec. G.233. [2] CCITT Recommendation Pilots on groups, supergroups, etc., Vol. III, Rec. G.241. [3] CCITT Recommendation Interruption control, Vol. VI, Rec. Q.416. [4] CCITT Recommendation Recommendations relating to the accuracy of carrier frequencies, Vol. III, Rec. G.225. [5] CCITT Recommendation Signal receiver, Vol. VI, Rec. Q.415. [6] CCITT Recommendation Signal sender, Vol. VI, Rec. Q.414. [7] CCITT Recommendation Digital line signalling code, Vol. VI, Rec. Q.421, 3.1.2. [8] CCITT Recommendation Conversion between analogue and digital versions of system R2 line signalling, Vol. VI, Rec. Q.430. [9] CCITT Recommendation Interruption control, Vol. VI, Rec. Q.416, 2.4.3.2 and 2.4.3.3. [10] CCITT Recommendation Pilots on groups, supergroups, etc., Vol. III, Rec. G.241, 1. [11] CCITT Recommendation Protection against the effect of faulty transmission on groups of circuits, Vol. VI, Rec. Q.33. Recommendation G.794 CHARACTERISTICS OF 24-CHANNEL TRANSMULTIPLEXING EQUIPMENTS (Malaga-Torremolinos, 1984, amended at Melbourne, 1988) 1 Introduction The 24-channel transmultiplexer is a transmultiplexing equipment which satisfies Recommendations G.791 and G.792 and provides interconnection between a digital signal at 1544 kbit/s and two analogue basic groups (24-channel TMUX-P). 42 Fascicle III.4 Rec. G.794

2 Digital interfaces 2.1 Coding law The coding law used is µ-law specified in Recommendation G.711. 2.2 Interfaces The 1544 kbit/s interfaces satisfy Recommendation G.703, 2. Fascicle III.4 Rec. G.794 43